The present invention relates to fluoroelastomer compositions based upon fluoropolymer blends, alloys, and fluoro/olefinic/polyvinylchloride polymer blends, as well as alloys with low smoke generation, low corrosivity, low heat release, flame retardancy and favorable char integrity with non-dripping characteristics. The preferred composition may be employed as insulation, insulation skin, jacket (sheath), buffer, crossweb (spline), shield, and/or separator materials in the manufacture of optical fiber or electrical wires and cables.
The present non-dripping, flame retardant insulative compositions are fluoroelastomers with nanocomposite and flame retardant additives. The present compositions can be melt processed to form extruded articles. Such manufacturing process and the resulting articles also constitute a portion of the inventive contribution disclosed herein.
It is known that the incorporation of nanocomposite additives into fluoroelastomeric compositions can improve some of properties of the compositions, particularly combustion properties including non-dripping characteristics. The nanocomposites that are suitable for incorporation into the present compositions are preferably by montmorillonites (the main fraction of the clay mineral bentonite), which are layered alumino-silicate or magnesium-silicate materials whose individual platelets measure on the order of one micron diameter, giving them an aspect ratio of about 1000:1. It is this morphology that leads to increased barrier properties to moisture, resistance of the composition to deformation, resistance to whitening or blooming, improved mechanical strength, sizeable drop in heat release rate and smoke properties, improved flame retardancy and char integrity of the polymer compositions. The nanocomposite additives are preferably chemically modified to increase the hydrophobicity of their surfaces, thereby enhancing their fire performance effectiveness. It is also known that blending or alloying fluoroelastomeric compositions with suitable olefinic or polyvinylchloride (PVC) polymers improves the flexibility, electrical properties, and manufacturing costs of the resulting blend or alloy. Suitable polymers to make the blends and alloys of the present compositions are: polytetrafluoroethylene (PTFE) fluorocarbons, fluorinated ethylene/propylene (FEP) fluorocarbons, perfluoroalkoxy (PFA) fluorocarbons, ethylene tetrafluoroethylene (ETFE) fluoropolymers, polyvinylidene (PVDF) fluoropolymers, ethylene chlorotrifluoroethylene (ECTFE) fluoropolymers, fluoro-chlorinated homopolymers, copolymers and terpolymers, very low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene propylene copolymer or rubber (EPR), ethyl vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA), and ethylene-based homopolymers, copolymers and terpolymers, and PVC-based homopolymers, copolymers and terpolymers.
The use of various flame retardant additives such as molybdates, metal hydrates, oxides, carbonates, talcs, clays, borates, stannates, phosphates, silicates, graphites, and carbon blacks will provide the resulting products with enhanced combustion properties.
The present fluoroelastomeric compositions may be crosslinked or grafted by any convenient method, such as by chemical crosslinking using organic peroxides, irradiation, and organosilanes or chemical grafting using acrylic and maleic acid.
The present thermoplastic fluoroelastomeric compositions have a high limiting oxygen index (LOI), and also burn with no visible smoke and/or dripping. The combination of favorable combustion, electrical and physical properties make the present compositions suitable for many applications such as cable components employed in market segments such as telecommunication, signal, power, industrial, and military cables.
The present non-dripping, flame retardant, fluoroelastomeric compositions comprise:
(a) a fluoropolymeric base polymer; and
(b) a nanoclay additive.
The preferred fluoropolymeric base polymer is selected from the group consisting of polytetrafluoroethylene (PTFE) fluorocarbons, fluorinated ethylene/propylene (FEP) fluorocarbons, perfluoroalkoxy (PFA) fluorocarbons, ethylene tetrafluoroethylene (ETFE) fluoropolymers, polyvinylidene (PVDF) fluoropolymers, ethylene chlorotrifluoroethylene (ECTFE) fluoropolymers, and fluoro-chlorinated homopolymers, copolymers and terpolymers.
The preferred composition further comprises at least one of an olefinic polymer, one of an acetate resin and an acrylate resin, and a polyvinylchloride resin.
The preferred olefinic polymer is selected from the group consisting of very low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), and ethylene propylene rubber (EPR). The group from which said olefinic polymer is selected can further consist of ethylene-based homopolymers, copolymers and terpolymers. The at least one olefinic polymer can be crosslinked, preferably using an organic peroxide.
The preferred one of an acetate resin and an acrylate resin is selected from the group consisting of ethyl vinyl acetate (EVA), ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), and ethylene butyl acrylate (EBA).
The preferred nanoclay additive is selected from the group consisting of synthetic silicate montmorillonites, natural layered silicate montmorillonites and a layered alumna-silicate. The individual platelets of the preferred nanoclay additive are approximately 1 micron in diameter. The nanoclay additive is preferably chemically modified to increase its hydrophobicity.
The preferred composition further comprises a filler selected from the group consisting of metal hydrates, oxides, carbonates, talcs, clays, molybdates, borates, stannates, carbon blacks, silicates, and phosphates.
The preferred composition may also further comprise an additive comprising at least one substance selected from the group consisting of an antioxidant, a pigment, and a lubricant.
A method for preparing an exfoliated thermoplastic elastomer blend of a fluoropolymer and a nanocomposite comprising dynamically mixing the fluoropolymer and the nanocomposite in a ratio of from about 99:1 to about 50:50 parts by weight, respectively. In the preferred method, at least one of an antioxidant, a lubricant and a pigment contacts said blend during mixing.